This invention relates in general to the tuning of a broadcast receiver, and more particularly relates to the tuning of a television receiver using a non-volatile memory for storing binary tune words that are electrically updated by a microcomputer type architecture control circuitry.
Previously developed electronic channel tuning systems have not been sufficiently flexible to enable wide-spread use for a variety of different types of television sets in applications. For example, certain previously developed systems have required extremely uniform varactor tuning diodes to enable channel tuning, thereby allowing insufficient tolerances for conventional variances between varactor diodes. Other previously developed systems have not been sufficiently modular to enable a selection of various types of channel access or displays. Moreover, previously developed electronic channel tuning systems have not been sufficiently economical to fabricate and have required uneconomical printed circuit boards or other uneconomical fabrication techniques for construction. For example, certain prior systems have required expensive potentiometers for each channel desired to be tuned. In addition, previously developed electronic television tuning systems have not satisfactorily satisfied recent regulatory requirements which call for a television tuner to provide a comparable capability and quality of tuning for both VHF and UHF stations. Specifically, such prior tuning systems have not enabled selection of precise UHF channels, nor have the prior systems provided means for easily changing selected UHF channels.
A major disadvantage in the channel tuning sections of television receivers has been the inability to electronically program and store tune voltages under all operating and non-operating conditions without using an auxiliary power source or a mechanically programmed memory. Existing electronically operable tuners use dedicated electronic circuitry to program tune voltage information in volatile memories where the volatile memories require batteries to provide standby power when the main power source is removed. The batteries are undesirable because they represent an additional cost to the manufacturer and a present a long-term tune voltage jeopardy if they fail when the main power source is removed. Memory loss due to battery failure can occur if there are poor battery connections, battery corrosion, or excessive battery drain. Other tuning systems use potentiometers to retain the channel tune voltage, but are also undesirable because they are not electronically alterable, and require a potentiometer for each channel to be tuned.
In accordance with the present invention, the undesirable characteristics are eliminated by using a nonvolatile DIFMOS memory matrix to store the channel tune voltages. The DIFMOS memory (dual injection floating gate MOS technology) is electronically alterable and has a projected memory retention capability of over 100 years with power removed. The control circuitry for the system uses a microcomputer type architecture to integrate the user control inputs and to generate the signals needed to access and alter the DIFMOS memory matrix. A principal advantage of this type of control compared to the dedicated control circuit approach is the ease with which different manufacturers' system requirements can be satisfied by simply reprogramming the algorithm of the instruction memory.
Accordingly, an object of the present invention is to provide an electronically programmable television tuning system having a non-volatile memory matrix for the storage of binary tune words.
Another object of the present invention is to provide electronic alterable tuning means for a broadcast receiver using a microcomputer approach, thereby eliminating the need for dedicated control circuitry.
Yet another object of the present invention is to provide means for electronically updating binary tune words of a selected channel in the tuning of a television receiver and for storing the updated binary words in a non-volatile memory matrix.
Still a further object of the present invention is to provide a means for generating a binary tune word corresponding to a selected UHF or VHF channel within the limits of a binary minimum and maximum word stored in a memory matrix.